A technique for controlling vibration of a golf club head has been developed to improve the hitting impression or adjust the hitting sound on impact. Japanese Patent Laid-Open No. 2004-313777 discloses a golf club head having a viscoelastic body. When the viscoelastic body is attached, the vibration on impact is absorbed by the viscoelastic body to improve the hitting impression and decrease the hitting sound that is offensive to the player's ear. Japanese Patent Laid-Open No. 2005-6763 discloses analyzing the vibration mode of a golf club head by a computer to correct the thickness and the like of the materials that form the golf club head. Japanese Patent Laid-Open No. 2003-102877 discloses providing a metal rib to a part corresponding to the antinode of the secondary bending vibration of a golf club head.
As such a method of controlling the vibration of a golf club head, the simplest is a method of mounting a viscoelastic body in a golf club head, as in Japanese Patent Laid-Open No. 2004-313777. Conventionally, the viscoelastic body may be mounted on the rear surface of the face portion because this is where the impact is input, or on the sole portion in order to lower the barycenter of the golf club. Not many studies have been made, however, on that portion to mount the viscoelastic body which is effective in vibration suppression. Therefore, the viscoelastic body may not exhibit its vibration suppressing function effectively.